Engineered Wood Products for Transportation Structures-An Overview of the Obstacles and Opportunities

Barry W. Dickson, Constructed Facilities Center, West Virginia University

Abstract mankind well for thousands of years. The opportunities for engineered wood products in the transportation field are numerous. Innovative bridges, In 18th and early 19th century America, our rural geotechnical structures, poles, and sight/sound barriers economy was heavily dependent on wood for fuel, are some of the existing opportunities. In all building, furniture, machinery, and probably thousands probability, more opportunities will emerge in the of other uses. Even then transportation was an essential future as engineered wood products become more portion of the economy, and wood was the material of versatile and durable. Unfortunately, some very real choice for most transportation structures. Some of our obstacles exist as well. Engineer’s perception of wood early wood bridges still stand today as a testament to as a second-class material, poorly executed designs and the durability and strength of wood structures when construction, and intense competition are only a few of designed and protected well. Later in our country’s the obstacles facing the industry. A workshop of history, railroads were the dominant force in the industry, government and research experts from the economy- wood products such as crossties, poles, and field of engineered wood products was held in bridge timbers allowed the railroads to transport heavy Morgantown, West Virginia in December 1994 to loads economically and quickly across the country. discuss the opportunities and obstacles facing the industry. The record created from the workshop The development of cast iron, steel, and eventually provides the basis for this paper. prestressed concrete in the late 19th and 20th centuries made wood products less desirable for some Keywords: Engineered wood products, bridges, transportation structures. In particular, bridges built of transportation structures these new materials were longer, stronger, and more durable than traditional wood bridges. In only a few Background decades the dominance of these newer materials was virtually complete. Not only was the use of wood for The use of wood for transportation structures is as old transportation structures decreased, but the skills as human history. Certainly our first bridges were logs required to use wood effectively diminished also. felled across streams. Readily available throughout Engineers and constructors were trained to work most of the world and easily worked, wood has served primarily with concrete and steel and the few wood

490 bridges that were built were often of poor design and groups for discussion, the meeting was divided into ten quality. workshops. Each workshop was assigned a topic and the experts were assigned to the workshops where their Many less visible markets for wood products in the expertise would be most useful. On the first day of the transportation field were retained, however. Wood meeting, workshops were held to discuss the railroad crossties were made much more durable with opportunities for and obstacles facing engineered wood the development of preservative treating techniques. in five applications-bridge superstructures; guide rails, Poles for the transport of electrical power and posts and poles; noise/sight barriers and communication lines sprung up in every comer of the formwork/falsework; retaining walls, piles, culverts, country. Timber piles continue to be used extensively and drop inlets; and repair and rehabilitation. On the for the support of bridge abutments and piers. second day, the experts were asked to form five Formwork and falsework are necessary for the different groups and confine their discussions to the construction of almost all transportation structures and issues related to material characterization; evaluation use large quantities of wood products. and design; construction; marketing and technology transfer: and environmental concerns. A Renaissance of Wood? With concrete, steel and a variety of structural plastic Each of the workshops’ leaders maintained a record of materials now available for the construction of the group discussions and made a brief presentation to transportation structures, why would today’s engineers the entire meeting to summarize the groups’ findings. choose wood? The answer is in both the old and the The following is a synopsis of the group leaders’ “new” properties of wood. Wood, as always, is light- presentations. weight, strong, and easily worked-properties which attract an engineer’s attention. Wood also is in plentiful Workshop 1- Bridge Superstructures supply and is likely to remain so. Our forests are Opportunities for the expansion of engineered wood remarkably resilient and, despite public opinion to the are abundant in the area of bridges. The USDA Forest contrary, “forest growth nationally has exceeded service’s Timber Bridge Initiative and the Intermodal harvest by 37% and the volume of forest growth was Surface Transportation Efficiency Act of 1991 have 350% greater than it had been in 1920”. (MacCleery, allowed several states to test the newest wood bridge 1995) The “new” properties of wood are a result of types. Innovative designs have been given years of technological advances to meet market needs. opportunities that they otherwise might never have Newly developed wood-based composites and had. The performance of the new bridges has been engineered wood products have strength, stiffness, mixed - some of the new wood bridges are performing durability, and reliability properties vastly superior to well and are reasonably cost-competitive, but others their sawn-lumber ancestors. The engineer’s choice of are not. The TBI has had a sufficient life-span to revise materials is no longer as clear-cut as it once was. and improve many of the original innovative designs. However, in order for this potentially large market to The Workshops be fully realized, the quality will have to be more In an attempt to expedite the use of new wood products consistent and the costs more competitive. engineered specifically for transportation structures, a workshop for interested engineers, manufacturers, Other opportunities for the expanded use of engineered researchers, and policy-makers was sponsored by the wood for bridges include: USDA Forest Service, State and Private Forestry. The l Newly developed engineered wood materials which Constructed Facilities Center of West Virginia have improved structural performance may be University administered and hosted the Engineered well-suited to bridge construction Wood for Transportation Workshop in December, l Improved prefabrication methods for wood bridge 1994. Workshop participants formed several working components have the potential to reduce costs groups and were asked to generate lists of l The public retains a preference for wood structures opportunities for and obstacles to the use of engineered in specific settings wood for various types of transportation structures. l Stress-laminated ballasted deck bridges for railroad The discussions of that meeting were recorded to trestle bridges generate a document, the Engineered Wood for Transportation Structures Workshop Record (CFC, Obstacles limiting the expanded use of engineered 1996). In order to organize the experts into productive wood for bridges include:

l A history of poorly engineered wood bridges which

491 has reduced many engineer’s confidence in l New wood-based composite materials like cement wood bonded wood l Environmental concerns resulting from improper l “Permanently” marked form materials that can be creosote treatment re-used more often than current products l Lack of comprehensive inspection methods and l Recently completed FHWA publications for accurate inspection devices construction and design of bridge temporary l Well-established competition from other materials works

Workshop 2- Guide Rails, Posts, and Poles Some of the obstacles cited to expanded use of The best properties of wood have long been utilized noise/sight barriers and formwork/falsework include: for posts and poles and, more recently, for guide rail l A history of poorly designed noise and sight barriers components. These properties include high strength has reduced engineers confidence in wood and energy absorbing characteristics. The greatest l Proprietary forming and falsework systems which opportunities for expansion of the market for guide have inconsistent design methods rails, posts, and poles exist in the timber producing areas where costs would be most competitive with Workshop 4 Retaining Walls, Piles, Culverts, and other materials. The expanding number of Drop Inlets “Greenways” (environmentally sensitive highways) The need for improved preservative methods and also should be a natural market for engineered wood consistent quality products were cited as the major guide rails, posts and poles. obstacles to expanded use of engineered wood for retaining walls, piles, culverts, and drop inlets (or other Other opportunities for guide rails, posts, and poles wood-based geotechnical structures). Opportunities of include: which the industry could take advantage are in the l Composite posts and poles which combine wood areas where the properties of wood, such as its non- and plastics corrosive nature, exceed those of competing materials. l New wood bridge rail designs that have been crash- An engineered wood culvert used in highly acidic tested and are now available for general use streams is one example.

Some of the obstacles cited to expanded use of Other opportunities for the expanded use of engineered engineered wood for guide rails, posts, and poles wood for geotechnical structures include: include: l Innovative prefabrication techniques resulting from l A lack of consistent design guides and design details the Timber Bridge Initiative which could (such as steel rail to wood rail transitions) decease first costs and reduce construction time

The large size of wood posts requires larger l New wood-based composites are becoming equipment to drive posts than is required for available which may increase the durability of competing materials geotechnical wood structures which must survive l A history of widely fluctuating prices for wood in very harsh environment posts and poles Some of the obstacles cited which limit the use of Workshop 3 & 6- Noise/Sight Barriers and geotechnical structures include:

Formwork/Falsework l The lack of standard plans

Potentially large markets exist for wood visual and l The difficulty of constructing durable connections acoustic highway screens. Recycled materials, and the cost of durable connections combined with wood products, could be used for many l The perception that wood products cannot be made of the components which form noise and sight barriers. to be durable in harsh environments The formwork/falsework field is currently the largest application area of engineered wood in the Workshop 5 Repair and Rehabilitation transportation market. The newly adopted LRFD code The basic challenge facing engineers whose for formwork and falsework will bring the design responsibility includes repair and rehabilitation of process to modem standards and could increase the use highway structures is to convert the connotation of of engineered wood products for this application. repair and rehabilitation from the negative to the positive. Other opportunities for noise/sight barriers and formwork/falsework include: Opportunities for repair and rehabilitation using

492 engineered wood include: seen by the workshop group as essential to expanded l Hardwood structural glued-laminated wood panels use of engineered wood. Specifically, the group noted have been tested for bridge deck applications the need for “proof loading” methods to evaluate wood and design guides are now available. structures, new non-destructive inspection methods, l Repair of transportation structures using wood and expanded education of engineers, and development of plastic composites standardized plans for engineered wood products.

Some of the obstacles cited which have limited the Opportunities for expanded use of engineered wood expanded use of engineered wood for repair and based on advances made in evaluation, analysis and rehabilitation include: design include: l Connecting wood or wood-based composites to l Recently completed standard plans for stress- other materials for repair is often difficult laminated bridges and hardwood glued l Very little design information or standard planning laminated bridges

is available l New design specifications in the American Association of State Highway and Workshop A- Material Characterization Transportation Officials Standard Specifications An accurate and consistent characterization of wood for Highway Bridges for stress-laminated wood and wood-based composites and the components made bridges of wood or wood based-composites is essential to the l The recent completion of several FHWA crash-tests expansion of wood markets. The combination of for wood rail systems engineered wood with other materials such as fiber reinforced plastics (FRP’s) may produce a material Some of the obstacles related to evaluation, analysis possessing exceptionally useful properties. The low and design which have limited the expanded use of cost, light weight, and availability of wood combined engineered wood for transportation include: with high strength and reliable properties of FRP could l The lack of standard plans for pedestrian bridges be applied to numerous highway structural l The need for more empirical data on the energy applications. adsorbing characteristics of wood so that this feature can be used more advantageously

Opportunities for expanded use of engineered wood l The need for more accurate inspection methods based on advances made in material characterization which will allow more precise evaluation of in- include: service wood structures l In-grade testing of various species and sizes of wood may add material choices for engineers Workshop C- Construction l Recent advances made to machine stress-rating and Because wood is a light-weight and relatively stress wave grading techniques should provide inexpensive material and most construction crews are more efficient use of wood resources familiar with it, the use of wood as a highway l More accurate design values for many hardwood structures material is generally accepted. The major species are now available obstacle facing the expanded use of engineered wood l Developments made in engineered wood for larger is the lack of industry-wide quality control standards. markets (such as housing) can often be The inherent variability of wood quality makes the converted to applications in transportation need for quality control even more necessary for wood products than for other materials. Some of the obstacles which limit the use of engineered wood include: Opportunities for expanded use of engineered wood l The continued difficulty of defining long-term based on advances made in construction include:

durability and structural performance of wood l Recent innovations in the prefabrication of wood products structures as a result of the Timber Bridge l Inherent properties of wood such as dimensional Initiative and the ISTEA of 1991

instability related to moisture changes l Many new engineered wood products are now available which reduce construction time and Workshop B- Evaluation, Analysis, and Design which are of higher quality than traditional sawn Although timber design has kept pace with the lumber advances made by other materials, the need for continued design and evaluation improvements was Some of the construction-related obstacles which limit

493 the use of engineered wood include: after its original service life l The lack of contractors with experience in heavy timber construction Some of the environmental and recycling obstacles l The lack of training aids for constructors which limit the use of engineered wood include:

specifically for wood transportation structures l Poor quality designs and specifications for wood structures have frequently led to environmental Workshop D and E- Economics, Marketing and problems and diminished engineer’s confidence

Technology Transfer l Composites manufactured of wood and other Marketing efforts for engineered wood products exist materials may be more difficult to recycle than for many applications. Engineered wood products such conventional wood products as bridges, noise/sight barriers and formwork are already commonplace but could be expanded. A The Next Step marketing strategy for these and other engineered Either explicitly or implicitly, each of the groups wood products should be based on a unified approach. recognized the need for actions to be taken to take Achieving a unified marketing strategy will require a advantage of opportunities available or to eliminate unification of the industry-something that has been obstacles. The need for actions requires another step in impossible to accomplish thus far. the process begun by this meeting. At the nearly- unanimous suggestion of the experts, a strategic Opportunities for expanded use of engineered wood planning committee comprised of 15 to 20 key persons based on advances made in marketing and technology in the engineered wood community was formed. The transfer include: strategic planning committee will has as its mission the l Establishment of the USDA Forest Service’s task of developing an action plan to implement the National Timber Bridge Information Resource resolutions of the expert group. Center l Studies of current market conditions for wood References bridges are now available MacCleery, Douglas. 1995. Resiliency: The trademark l Large increase in the amount of technical support of American Forests. Forest Products Journal. 45(l): information available 19-28 Some of the obstacles which limit the use of CFC. 1996. Engineered wood for transportation engineered wood include: structures workshop. CFC Report 96-232. l The lack of consistent wood terminology hampers Morgantown, WV. Constructed Facilities Center clear communication of technical information l The belief on the part of many engineers in the American Association of State Highway “second-class” nature of wood for structural Transportation Officials. Standard Specification for applications Highway Bridges. Fifteenth Edition. 1992. Washington, D.C. Workshop F-Environmental Like the repair and rehabilitation group, the Acknowledgments environmental group found that the most pressing The author wishes to acknowledge the financial and challenge was to change the perception that technical support of the USDA Forest Service, Timber preservative treated wood products are an Bridge Information Resource Center for the workshop environmental liability. Providing preservative treated which generated the material for this paper. Additional wood products users as well as the general public with funds and technical contributions were provided by the facts about wood preservatives should be the Burke-Parsons-Bowlby Corporation, Trus Joist highest priority for the engineered wood products MacMillan, and the American Plywood Association. industry. The many experts who contributed their time and experience to the workshop deserve most of the credit Opportunities for expanded use of engineered wood for this paper. based on advances made environmental include: l The perception of wood as an “environmentally friendly” material can be used advantageously to promote wood l Wood has the potential to be re-used or recycled

494 In: Ritter, M.A.; Duwadi, S.R.; Lee, P.D.H., ed(s). National conference on wood transportation structures; 1996 October 23-25; Madison, WI. Gen. Tech. Rep. FPL- GTR-94. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.